New Optogenetic Tool Allows Researchers to Control and Visualize Receptor Signals in Neural Cells

An innovative optogenetic tool allows researchers to effectively control, replicate, and envisage serotonin receptor signals existing in neural cells.

In this regard, the researchers altered the eye’s photosensitive membrane receptor called melanopsin. As a consequence, they can apply light to switch the receptor on and off. The receptor also behaved similarly to a sensor indicating if the cell’s specific signaling pathways had been activated through fluorescence. In addition, the sensor was particularly developed to move to those domains in the neural cells that are especially sensitive to serotonin—a neurotransmitter. The research team from Ruhr-Universität Bochum, led by Dennis Eickelbeck and Professor Stefan Herlitze, has described the study in the journal Nature Communications Biology on February 14^th, 2019.

Activating signaling pathways with light

Specific signaling pathways in the cells can be controlled by the G-protein-coupled receptor, melanopsin. In previous research, the research team at the Department of General Zoology and Neurobiology in Bochum had used the melanopsin receptor as an optogenetic tool. The biologists—after modifying the receptor—were able to turn it off with yellow light and on with blue light. Therefore, the team can possibly use light to stimulate numerous G-protein-coupled signaling pathways existing in neural cells.

In their latest work, the researchers further improved the tool and converted it into a sensor, which shows whether a G-protein-coupled signaling pathway has been turned on or not. Here, the trick is once a signaling pathway like this is triggered, the calcium ion concentration in the cell increases. The team combined melanopsin with a calcium indicator protein, the fluorescence intensity of which increases after an increase in the concentration of calcium in the cell. Therefore, the activation of a G-protein-coupled signaling pathway is indicated by green light.

Dual color code

The biologists then added a couple of additional functions to their sensor, that is, the calcium-melanopsin-local-sensor, abbreviated as Camello. They combined a second fluorescent protein that continuously produces red fluorescence. By tracking the red light, the biologists were able to identify the sensor in the cells, irrespective of whether a signaling pathway was turned on or not. Thus, a red light showed the presence of the Camello sensor, while an additional green light indicated that it had triggered the signaling pathways.

Receptor trafficking in specific domains

The team finally added a piece of a serotonin receptor to Camello. As a consequence, the sensor was transferred to those specific domains of the cell, in which serotonin receptors happen naturally.

Since serotonin is involved in numerous processes in the central nervous system, it also plays an important role in many disorders, such as depression, schizophrenia, anxiety and migraine. We are hoping that, by facilitating detailed research into the transport, localisation and activity of relevant receptors, our tool will help us understand the mechanisms underlying these diseases.

Dennis Eickelbeck, Department of General Zoology and Neurobiology, Ruhr-Universität Bochum.

Cooperation partners

For the purpose of the study, the Department of General Zoology and Neurobiology partnered with colleagues from the Developmental Neurobiology research group, the Neural Computation Institute, and the Department of Biophysics at Ruhr-Universität Bochum.

Funding

The research was funded by the German Research Foundation in the projects He2471/23-1, He2471/21-1 and He2471/19-1, the SPP 1926 Priority Programme, Collaborative Research Centre SFB 874 (project no. 122679504) and SFB 1280 (project no. 316803389) and the Ma5806/2-1 project. Additional funding was supplied by Schram-Stiftung, Studienstiftung des deutschen Volkes, Friedrich Ebert Foundation and Wilhelm-und-Günter-Esser-Stiftung.